When the French recruited the Ottowas, Potowatomis and Abenakis to fight in the battle for the fort, they promised them the opportunity to plunder the fort after the battle was won. This clause was crucial to the Indians because a number of devastating forces-including smallpox and starvation brought on by the disruptions of European settlers and the war—made every opportunity to get food, supplies, and money crucial for their survival. Indians were not usually paid by either the British or the French, except in gifts of rum, blankets, clothing, and trade goods. Depending on the Indian nation, "plunder" might be interpreted as including the opportunity to gather scalps from the enemy. As they had at Oswego, the French usually turned their backs while the Indians engaged in their scalping.
But at Fort William Henry, the French made other plans. In their negotiations with the British as to rights of surrender, they allowed the British to remove most of their personal belongings and goods from the fort. No Indians were present at these negotiations. As the troops filed out of the fort with all of their supplies, the Indians grew infuriated. The British were leaving with their only spoils of war, and it appeared as though the French had deceived them. The Indians reacted violently, by attacking the helpless sick and wounded at the end of the train, and chaos quickly broke out.
The Indians who seized scalps from the sick at the back of the train were indeed punished brutally for their actions—the scalps were infected with smallpox, which was transferred to the Indians and their communities, further weakening the Indians. But both the British and colonials used the massacre for years after the war as an example of the "savagery" of the Indians and a justification for seizing their lands. The truth, unfortunately, isn't quite so simple.